Two-stage-to-orbit
Encyclopedia
A two-stage-to-orbit launch vehicle
is a spacecraft in which two distinct stages
provide propulsion consecutively in order to achieve orbital velocity. It is intermediate between a three-stage-to-orbit
launcher and a hypothetical single-stage-to-orbit
(SSTO) launcher.
At liftoff the first stage is responsible for accelerating the vehicle. At some point the second stage detaches from the first stage and continues to orbit under its own power.
An advantage of such a system over single-stage-to-orbit is that the entire mass of the spacecraft is not carried into orbit. This reduces the difficulty involved in reaching orbital velocity.
An advantage over three or more stages is reduction in complexity and fewer separation events, each of which reduces cost and risk of failure.
It is not always clear when a vehicle is a DSTO. Many designs which use a very small boost at the beginning of their flight are referred to as single-stage-to-orbit. Some have also coined the expression 1.5STO for 'one-and-a-half-stage-to-orbit', e.g., the Atlas. Also, many launch vehicles have side-mounted booster rockets which are jettisoned early which are called "stage-0".
this approach is often proposed as an alternative to single-stage-to-orbit (or SSTO). Its supporters argue that, since each stage may have a lower mass ratio
than an SSTO launch system, such a system may be built without approaching as close to the limitations of its structural materials. It therefore should require less maintenance, less testing, experience fewer failures and have a longer working life.
Critics argue that the increased complexity of designing two separate stages that must interact, the logistics involved in returning the first stage to the launch site, and the difficulties of conducting incremental testing on a second stage will outweigh these benefits. In the case of airplane-like lower stages they also argue how difficult and expensive high speed aircraft (like the SR-71
) are to develop and operate, and question performance claims. Many 'mini-shuttle' designs that use transport aircraft as first stages also face similar problems with ice/foam as the Space Shuttle
due to the requirement they also carry a large external tank for their fuel.
On the other hand, the two-stage approach allows the lower stage to be optimized for operation in the Earth's lower atmosphere, where pressure and drag are high, while the upper stage can be optimized for operation in the near-vacuum conditions of the later part of the launch. This allows an increase in the payload mass fraction of a two-stage vehicle over single-stage or stage-and-a-half vehicles, which have to perform in both environments using the same hardware.
or VTOHL
aircraft. The DC-X has proven the VTOL option design workable. Other designs like the DH-1
concept take it a step further and use a 'pop-up/pop-down' approach, which delivers the orbiting stage to a point about 60 km above the earth's surface, before dropping down to the launch pad again. In the case of the DH-1
, the upper stage is effectively an 'almost SSTO' with a more realistic mass fraction and which was optimised for reliability.
-like first stage and a rocket
-like second stage. The airplane elements can be wings, air-breathing engines, or both. This approach appeals because it transforms Earth's atmosphere
from an obstacle into an advantage. Above a certain speed and altitude, wings and scramjet
s cease being effective, and the rocket is deployed to complete the trip to orbit.
While not an orbital vehicle, the successful private SpaceShipOne suborbital spacecraft developed for the Ansari X Prize
demonstrated that the problems of integrating a two-stage system, with a winged aircraft as the "lower half", that can reach the edge of space are not insurmountable. , the team behind SpaceShipOne is working on a commercial sub-orbital launch system -- SpaceShipTwo -- based on this technology.
that an XB-70-type first stage, with an X-20 spacecraft, possibly manned, may have reached low earth orbit. However, information on this system remains conjectural.
Rocket launch
A rocket launch is the takeoff phase of the flight of a rocket. Launches for orbital spaceflights, or launches into interplanetary space, are usually from a fixed location on the ground, but may also be from a floating platform such as the San Marco platform, or the Sea Launch launch...
is a spacecraft in which two distinct stages
Multistage rocket
A multistage rocket is a rocket that usestwo or more stages, each of which contains its own engines and propellant. A tandem or serial stage is mounted on top of another stage; a parallel stage is attached alongside another stage. The result is effectively two or more rockets stacked on top of or...
provide propulsion consecutively in order to achieve orbital velocity. It is intermediate between a three-stage-to-orbit
Three-stage-to-orbit
The three-stage-to-orbit launch system is a commonly used rocket system to attain Earth orbit. The spacecraft uses three distinct stages to provide propulsion consecutively in order to achieve orbital velocity.-Examples of three stage to orbit systems:...
launcher and a hypothetical single-stage-to-orbit
Single-stage-to-orbit
A single-stage-to-orbit vehicle reaches orbit from the surface of a body without jettisoning hardware, expending only propellants and fluids. The term usually, but not exclusively, refers to reusable vehicles....
(SSTO) launcher.
At liftoff the first stage is responsible for accelerating the vehicle. At some point the second stage detaches from the first stage and continues to orbit under its own power.
An advantage of such a system over single-stage-to-orbit is that the entire mass of the spacecraft is not carried into orbit. This reduces the difficulty involved in reaching orbital velocity.
An advantage over three or more stages is reduction in complexity and fewer separation events, each of which reduces cost and risk of failure.
Examples of two stage to orbit systems
- Angara (LEO) future
- Atlas VAtlas VAtlas V is an active expendable launch system in the Atlas rocket family. Atlas V was formerly operated by Lockheed Martin, and is now operated by the Lockheed Martin-Boeing joint venture United Launch Alliance...
(401 and 501) - Cosmos-3MCosmos-3MThe Kosmos-3M is a Russian space launch vehicle. It is a liquid-fueled two-stage rocket, first launched in 1967 and with over 420 successful launches to its name. The Cosmos 3M uses nitrogen tetroxide as an oxidizer to lift roughly 1400 kg of payload into orbit...
- Delta IV (medium)
- Falcon 1Falcon 1The Falcon 1 is a partially reusable launch system designed and manufactured by SpaceX, a space transportation company in Hawthorne, California. The two-stage-to-orbit rocket uses LOX/RP-1 for both stages, the first powered by a single Merlin engine and the second powered by a single Kestrel engine...
- Falcon 9Falcon 9Falcon 9 is a rocket-powered spaceflight launch system designed and manufactured by SpaceX. Both stages of its two-stage-to-orbit vehicle use liquid oxygen and rocket-grade kerosene propellants...
- Saturn IBSaturn IBThe Saturn IB was an American launch vehicle commissioned by the National Aeronautics and Space Administration for use in the Apollo program...
- Saturn INT-21Saturn INT-21The Saturn INT-21 was a study for an American orbital launch vehicle of the 1970s. It was derived from the Saturn V rocket used for the Apollo program, using its first and second stages, but lacking the third stage. The guidance unit would be moved from the top of the third stage to the top of the...
- Tsyklon-2Tsyklon-2The Tsyklon-2, also known as Tsiklon-2 and Tsyklon-M, GRAU index 11K69, was a Soviet, and subsequently Ukrainian orbital carrier rocket. A derivative of the R-36 ICBM, and a member of the Tsyklon family, it made its maiden flight on 6 August 1969, and after 106 launches, made its final flight on 24...
- Zenit-2Zenit-2The Zenit-2 is a Ukrainian, previously Soviet, expendable carrier rocket. First flown in 1985, it has been launched 37 times, with six failures. It is a member of the Zenit family of rockets, and was designed by the Yuzhnoye Design Bureau. A modified version, the Zenit-2S, is used as the first two...
- Blackstar (spacecraft) conjectural system
It is not always clear when a vehicle is a DSTO. Many designs which use a very small boost at the beginning of their flight are referred to as single-stage-to-orbit. Some have also coined the expression 1.5STO for 'one-and-a-half-stage-to-orbit', e.g., the Atlas. Also, many launch vehicles have side-mounted booster rockets which are jettisoned early which are called "stage-0".
Reusable launch systems
With reference to a reusable launch systemReusable launch system
A reusable launch system is a launch system which is capable of launching a launch vehicle into space more than once. This contrasts with expendable launch systems, where each launch vehicle is launched once and then discarded.No true orbital reusable launch system is currently in use. The...
this approach is often proposed as an alternative to single-stage-to-orbit (or SSTO). Its supporters argue that, since each stage may have a lower mass ratio
Mass ratio
In aerospace engineering, mass ratio is a measure of the efficiency of a rocket. It describes how much more massive the vehicle is with propellant than without; that is, it is the ratio of the rocket's wet mass to its dry mass...
than an SSTO launch system, such a system may be built without approaching as close to the limitations of its structural materials. It therefore should require less maintenance, less testing, experience fewer failures and have a longer working life.
Critics argue that the increased complexity of designing two separate stages that must interact, the logistics involved in returning the first stage to the launch site, and the difficulties of conducting incremental testing on a second stage will outweigh these benefits. In the case of airplane-like lower stages they also argue how difficult and expensive high speed aircraft (like the SR-71
SR-71 Blackbird
The Lockheed SR-71 "Blackbird" was an advanced, long-range, Mach 3+ strategic reconnaissance aircraft. It was developed as a black project from the Lockheed A-12 reconnaissance aircraft in the 1960s by the Lockheed Skunk Works. Clarence "Kelly" Johnson was responsible for many of the...
) are to develop and operate, and question performance claims. Many 'mini-shuttle' designs that use transport aircraft as first stages also face similar problems with ice/foam as the Space Shuttle
Space Shuttle
The Space Shuttle was a manned orbital rocket and spacecraft system operated by NASA on 135 missions from 1981 to 2011. The system combined rocket launch, orbital spacecraft, and re-entry spaceplane with modular add-ons...
due to the requirement they also carry a large external tank for their fuel.
On the other hand, the two-stage approach allows the lower stage to be optimized for operation in the Earth's lower atmosphere, where pressure and drag are high, while the upper stage can be optimized for operation in the near-vacuum conditions of the later part of the launch. This allows an increase in the payload mass fraction of a two-stage vehicle over single-stage or stage-and-a-half vehicles, which have to perform in both environments using the same hardware.
Helicopter-like first stage
Taking the view that airplane like operations do not translate to airplane-like appearance, many TSTOs have first stages that operate as VTOLVTOL
A vertical take-off and landing aircraft is one that can hover, take off and land vertically. This classification includes fixed-wing aircraft as well as helicopters and other aircraft with powered rotors, such as cyclogyros/cyclocopters and tiltrotors...
or VTOHL
VTOHL
Vertical take-off and horizontal landing is an aircraft that can lift off vertically but land in the traditional manner.While many VTOL aircraft can operate in this fashion, some planes must land normally after taking off vertically due to a vertical landing either being impossible or impractical...
aircraft. The DC-X has proven the VTOL option design workable. Other designs like the DH-1
DH-1
This page refers to the DH-1 rocket proposal, not the Airco DH.1.The DH-1 is a reusable two stage to orbit rocket proposed in the book The Rocket Company by Patrick J. G. Stiennon, David M. Hoerr, Doug Birkholz . The concept is patented...
concept take it a step further and use a 'pop-up/pop-down' approach, which delivers the orbiting stage to a point about 60 km above the earth's surface, before dropping down to the launch pad again. In the case of the DH-1
DH-1
This page refers to the DH-1 rocket proposal, not the Airco DH.1.The DH-1 is a reusable two stage to orbit rocket proposed in the book The Rocket Company by Patrick J. G. Stiennon, David M. Hoerr, Doug Birkholz . The concept is patented...
, the upper stage is effectively an 'almost SSTO' with a more realistic mass fraction and which was optimised for reliability.
Airplane-like first stage
TSTO designs comprise an airplaneFixed-wing aircraft
A fixed-wing aircraft is an aircraft capable of flight using wings that generate lift due to the vehicle's forward airspeed. Fixed-wing aircraft are distinct from rotary-wing aircraft in which wings rotate about a fixed mast and ornithopters in which lift is generated by flapping wings.A powered...
-like first stage and a rocket
Rocket
A rocket is a missile, spacecraft, aircraft or other vehicle which obtains thrust from a rocket engine. In all rockets, the exhaust is formed entirely from propellants carried within the rocket before use. Rocket engines work by action and reaction...
-like second stage. The airplane elements can be wings, air-breathing engines, or both. This approach appeals because it transforms Earth's atmosphere
Earth's atmosphere
The atmosphere of Earth is a layer of gases surrounding the planet Earth that is retained by Earth's gravity. The atmosphere protects life on Earth by absorbing ultraviolet solar radiation, warming the surface through heat retention , and reducing temperature extremes between day and night...
from an obstacle into an advantage. Above a certain speed and altitude, wings and scramjet
Scramjet
A scramjet is a variant of a ramjet airbreathing jet engine in which combustion takes place in supersonic airflow...
s cease being effective, and the rocket is deployed to complete the trip to orbit.
While not an orbital vehicle, the successful private SpaceShipOne suborbital spacecraft developed for the Ansari X Prize
Ansari X Prize
The Ansari X Prize was a space competition in which the X Prize Foundation offered a US$10,000,000 prize for the first non-government organization to launch a reusable manned spacecraft into space twice within two weeks...
demonstrated that the problems of integrating a two-stage system, with a winged aircraft as the "lower half", that can reach the edge of space are not insurmountable. , the team behind SpaceShipOne is working on a commercial sub-orbital launch system -- SpaceShipTwo -- based on this technology.
Secret System Orbited?
It has been suggested by Aviation Week & Space TechnologyAviation Week & Space Technology
Aviation Week & Space Technology, often abbreviated Aviation Week or AW&ST, is a weekly magazine owned and published by McGraw-Hill...
that an XB-70-type first stage, with an X-20 spacecraft, possibly manned, may have reached low earth orbit. However, information on this system remains conjectural.